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Abstract:

A nonaqueous electrolyte battery includes a positive electrode, a
negative electrode and a nonaqueous electrolyte. The negative electrode
contains a lithium compound and a negative electrode current collector
supporting the lithium compound. A log differential intrusion curve
obtained when a pore size diameter of the negative electrode is measured
by mercury porosimetry has a peak in a pore size diameter range of 0.03
to 0.2 μm and attenuates with a decrease in pore size diameter from an
apex of the peak. A specific surface area (excluding a weight of the
negative electrode current collector) of pores of the negative electrode
found by mercury porosimetry is 6 to 100 m2/g. A ratio of a volume
of pores having a pore size diameter of 0.05 μm or less to a total
pore volume is 20% or more.

Claims:

1. A nonaqueous electrolyte battery comprising: a positive electrode; a
negative electrode containing a lithium compound and a negative electrode
current collector supporting the lithium compounds; and a nonaqueous
electrolyte, wherein a log differential intrusion curve obtained when a
pore size diameter of the negative electrode is measured by mercury
porosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μm
and attenuates with a decrease in pore size diameter from an apex of the
peak, a specific surface area (excluding a weight of the negative
electrode current collector) of pores of the negative electrode found by
mercury porosimetry is 6 to 100 m2/g, and a ratio of a volume of
pores having a pore size diameter of 0.05 μm or less to a total pore
volume is 20% or more.

2. The nonaqueous electrolyte battery according to claim 1, wherein a
volume of pores measured by the mercury porosimetry is 0.1 to 0.5 mL per
1 g of the negative electrode, excluding the negative electrode current
collector.

3. The nonaqueous electrolyte battery according to claim 1, wherein the
lithium compound includes lithium-titanium oxide.

4. The nonaqueous electrolyte battery according to claim 3, wherein the
lithium-titanium oxide has a spinel structure or a ramsdellite structure.

5. The nonaqueous electrolyte battery according to claim 1, wherein the
peak exists in a pore size diameter range of 0.04 to 0.1 μm.

6. The nonaqueous electrolyte battery according to claim 1, wherein the
ratio is 20 to 90%.

7. A battery pack comprising a nonaqueous electrolyte battery, the
nonaqueous electrolyte battery comprising: a positive electrode; a
negative electrode containing a lithium compound and a negative electrode
current collector supporting the lithium compound; and a nonaqueous
electrolyte, wherein a log differential intrusion curve obtained when a
pore size diameter of the negative electrode is measured by mercury
porosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μm
and attenuates with a decrease in pore size diameter from an apex of the
peak, a specific surface area (excluding a weight of the negative
electrode current collector) of pores of the negative electrode found by
mercury porosimetry is 6 to 100 m2/g, and a ratio of a volume of
pores having a pore size diameter of 0.05 μm or less to a total pore
volume is 20% or more.

8. The battery pack according to claim 7, wherein a volume of pores
measured by mercury porosimetry is 0.1 to 0.5 mL per 1 g of the negative
electrode, excluding the negative electrode current collector.

9. The battery pack according to claim 7, wherein the lithium compound
includes lithium-titanium oxide.

10. The battery pack according to claim 9, wherein the lithium-titanium
oxide has a spinel structure or a ramsdellite structure.

11. The battery pack according to claim 7, wherein the peak exists in a
pore size diameter range of 0.04 to 0.1 μm.

12. The battery pack according to claim 7, wherein the ratio is 20 to
90%.

13. A vehicle comprising the nonaqueous electrolyte battery according to
claim 1.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of, and claims the
benefit of priority under 35 U.S.C. §120, from U.S. application Ser.
No. 13/686,501, filed Nov. 27, 2012, which is a continuation of U.S.
application Ser. No. 12/047,708, filed Mar. 13, 2008, now U.S. Pat. No.
8,343,667, issued on Jan. 1, 2013, which claims the benefit of priority
under 35 U.S.C. §119, from Japanese Patent Application No.
2007-085716, filed Mar. 28, 2007, the entire contents of each of which
are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a nonaqueous electrolyte battery,
and a battery pack and a vehicle provided with this nonaqueous
electrolyte battery.

[0004] 2. Description of the Related Art

[0005] As shown in JP-A 5-151953 (KOKAI) and JP-A 2006-59690 (KOKAI), it
is known that an improvement in the performance of a battery can be
attained by knowing the state of particles in the battery electrode based
on the measurement of the pore distribution of the battery electrode by
using mercury porosimetry. In this case, JP-A 5-151953 (KOKAI) relates to
an invention using, as the negative electrode active material, a mixture
of a metal oxide and an insoluble and infusible base of a polyacene type
skeleton structure having a specific surface area of 600 m2/g or
more as measured by a BET method. On the other hand, JP-A 2006-59690
(KOKAI) relates to an invention using, as the negative electrode active
material, a composite graphite material having a relatively small
specific surface area of 1.5 to 5 m2/g as measured by a BET method.

[0006] When a lithium compound having a small ionic diffusibility in a
solid is used as the negative electrode active material, it is difficult
to develop a high power battery. However, it is known that high power can
be attained by using microparticles of this lithium compound. These
microparticles of a lithium compound pose the problem that they cause a
large variation in the output characteristics of a battery depending on
the production method of the battery, because they have the
characteristic that they tend to be coagulated in a process of producing
an electrode using these microparticles.

[0007] The nonaqueous electrolyte battery described in JP-A 2007-18882
(KOKAI) uses, as the negative electrode active material, lithium compound
particles having a lithium ion absorption potential of 0.4V (vs.
Li/Li.sup.+) or more and an average particle diameter of 1 μm or less.
In JP-A 2007-18882 (KOKAI), during the manufacture of a negative
electrode, a slurry is stirred strongly in a specified condition to
reduce coagulation among lithium compound particles. It is described in
JP-A 2007-18882 (KOKAI) that the edges of lithium compound particles are
scraped away by this stirring to smooth the surfaces of these particles.
JP-A 2007-18882 (KOKAI) also describes that, as a result, these lithium
compound particles can be filled at a high density in a negative
electrode. Therefore, the pore size diameter distribution is shifted to
the smaller pore size diameter side, with the result that a first peak
having a mode diameter of 0.01 to 0.2 μm and a second peak having a
mode diameter of 0.003 to 0.02 μm appear in the log differential
intrusion curve of the negative electrode, as measured using mercury
porosimetry. JP-A 2007-18882 (KOKAI) describes that the cycle life of a
nonaqueous electrolyte battery is improved by specifying the pore volume
in each peak range.

BRIEF SUMMARY OF THE INVENTION

[0008] According to a first aspect of the present invention, there is
provided a nonaqueous electrolyte battery, comprising:

[0009] a positive electrode;

[0010] a negative electrode containing a lithium compound and a negative
electrode current collector supporting the lithium compound; and

[0011] a nonaqueous electrolyte,

[0012] wherein a log differential intrusion curve obtained when a pore
size diameter of the negative electrode is measured by mercury
porosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μm
and attenuates with a decrease in pore size diameter from an apex of the
peak,

[0013] a specific surface area (excluding a weight of the negative
electrode current collector) of pores of the negative electrode found by
mercury porosimetry is 6 to 100 m2/g, and

[0014] a ratio of a volume of pores having a pore size diameter of 0.05
μm or less to a total pore volume is 20% or more.

[0015] According to a second aspect of the present invention, there is
provided a battery pack comprising a nonaqueous electrolyte battery, the
nonaqueous electrolyte battery comprising:

[0016] a positive electrode;

[0017] a negative electrode containing a lithium compound and a negative
electrode current collector supporting the lithium compound; and

[0018] a nonaqueous electrolyte,

[0019] wherein a log differential intrusion curve obtained when a pore
size diameter of the negative electrode is measured by mercury
porosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μm
and attenuates with a decrease in pore size diameter from an apex of the
peak,

[0020] a specific surface area (excluding a weight of the negative
electrode current collector) of pores of the negative electrode found by
mercury porosimetry is 6 to 100 m2/g, and

[0021] a ratio of a volume of pores having a pore size diameter of 0.05
μm or less to a total pore volume is 20%; or more.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0022] FIG. 1 is a characteristic curve showing the pore size diameter
distribution of a negative electrode used in a nonaqueous electrolyte
battery according to a first embodiment when the pore size diameter
distribution is measured using mercury porosimetry;

[0023] FIG. 2 is a partially broken perspective view showing a nonaqueous
electrolyte battery according to the first embodiment;

[0024] FIG. 3 is a partially broken perspective view showing another
nonaqueous electrolyte battery according to the first embodiment;

[0025] FIG. 4 is a pattern diagram of an enlarged section of the part
shown by A in the nonaqueous electrolyte battery shown in FIG. 3;

[0026] FIG. 5 is a perspective view showing a typical electrode group
having a laminate structure used in a nonaqueous electrolyte battery
according to the first embodiment;

[0027] FIG. 6 is a partially broken perspective view showing a nonaqueous
electrolyte battery according to the first embodiment;

[0028] FIG. 7 is an explosion perspective view of a battery pack according
to a second embodiment;

[0029] FIG. 8 is a block diagram showing an electric circuit of a battery
pack shown in FIG. 7;

[0030] FIG. 9 is a pattern diagram showing a series hybrid car according
to a third embodiment;

[0031] FIG. 10 is a pattern diagram showing a parallel hybrid car
according to the third embodiment;

[0032] FIG. 11 is a pattern diagram showing a series-parallel hybrid car
according to the third embodiment;

[0033] FIG. 12 is a pattern diagram showing a car according to the third
embodiment;

[0034] FIG. 13 is a pattern diagram showing a hybrid motorcycle according
to the third embodiment;

[0035] FIG. 14 is a pattern diagram showing an electric motorcycle
according to the third embodiment;

[0036] FIG. 15 is a pattern diagram showing a rechargeable vacuum cleaner
according to a fourth embodiment; and

[0037] FIG. 16 is a structural view of a rechargeable vacuum cleaner
according to FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The inventors of the present invention have made earnest studies to
improve the output performance of a nonaqueous electrolyte battery using
a lithium compound as the negative electrode active material and as a
result, found that a high output performance is obtained when the pore
size diameter distribution of the negative electrode as measured using
mercury porosimetry satisfies the following conditions (1) to (4).

[0039] (1) The log differential intrusion curve of the negative electrode
measured using mercury porosimetry has a peak in a pore size diameter
range of 0.03 μm to 0.2 μm.

[0040] (2) The above log differential intrusion curve attenuates with a
decrease in pore size diameter from the apex of the above peak.

[0041] (3) The specific surface area of pores measured using the above
mercury porosimetry is 6 m2/g or more and 100 m2/g or less. In
this case, the weight of the negative electrode which is used to
calculate the specific surface area of pores is a value excluding the
weight of the negative electrode current collector.

[0042] (4) The ratio of the volume of pores having a pore size diameter of
0.05 μm or less to the total pore volume is 20% or more. The above
ratio is found by mercury porosimetry.

[0043] A negative electrode which satisfies the above condition (3) is
superior in nonaqueous electrolyte impregnation ability. It is desirable
to use lithium compound particles having a fine particle size to satisfy
the above condition (3). However, if the particle size of lithium
compound particles is smaller, a flock tends to be produced in a process
of producing the negative electrode. A negative electrode which satisfies
the above conditions (1), (2) and (4) is reduced not only in the amount
of this flock but also in the amount of broken pieces of primary
particles of the lithium compound and therefore, the uniformity of the
distribution of a negative electrode active material can be improved.
Therefore, because the nonaqueous electrolyte impregnation ability of the
negative electrode and the uniformity of the distribution of the negative
electrode active material can be improved, the DC resistance of the
negative electrode is reduced and therefore, the output performance of
the nonaqueous electrolyte battery is improved.

[0044] FIG. 1 shows an example of a distribution curve of pore volume of
the negative electrode which is measured by mercury porosimetry. In FIG.
1, the abscissa is the pore size diameter (radius), the right ordinate is
the log differential intrusion and the left ordinate is the cumulative
intrusion. The log differential intrusion curve is a curve expressed by
the right ordinate to show a variation in the log differential intrusion
as a function of the pore size diameter. As shown in FIG. 1, a peak
exists in a pore size diameter range of 0.03 μm to 0.2 μm. Also,
the curve attenuates with a decrease in pore size diameter from the apex.
In other words, no other peak is present at a pore size diameter smaller
than the pore size diameter of the apex of the peak. Here, the
description "a peak exists in a pore size diameter range of 0.03 μm to
0.2 μm" means that the mode diameter of the peak which is the pore
size diameter of the apex of the peak is 0.03 μm or more and 0.2 μm
or less. The pore size diameter is more preferably 0.04 μm or more and
0.1 μm or less.

[0045] The curve defined by the left ordinate indicates the integrating
volume obtained by integrating the volumes of pores having a pore size
diameter of 100 μm or less in the direction of a reduction in pore
size diameter, that is, a cumulative intrusion. The maximum value V1
of the cumulative intrusion in the cumulative intrusion curve corresponds
to the total pore volume of the negative electrode. The volume of pores
having pore size diameters of 0.05 μm or less is a difference between
the maximum value V1 (total pore volume) of the cumulative intrusion
and the cumulative intrusion V2 at a pore size diameter of 0.05
μm. The ratio of the volume of pores having a pore size diameter of
0.05 μm or less to the total pore volume is preferably 20% or more and
more preferably 30% or more. Also, the upper limit of the ratio may be
designed to be 90%. The reason for this is because if a negative
electrode is used which is provided with pores mostly having a small
diameter, as in the case where the ratio of pores having a pore size
diameter of 0.05 μm or less exceeds 90%, there is a concern that the
negative electrode active material detaches from the current collector
metal foil because it becomes less resistant to mechanical bending and to
expansion and shrinkage thereof during charging and discharging.

[0046] If, among the above conditions (1), (2) and (4), any condition is
unsatisfied, the negative electrode is greatly deteriorated in output
performance because the uniformity in the distribution of a negative
electrode active material in the negative electrode is reduced.

[0047] Further, the total pore volume is preferably in the range of 0.1 to
0.5 mL/g per 1 g of the negative electrode, excluding the negative
electrode current collector. When the total pore volume is less than 0.1
mL/g, there is a concern that a high output performance is not obtained
because only an insufficient reaction field is obtained on the surface of
the electrode. When the total pore volume is larger than 0.5 mL/g, on the
other hand, side reactions other than the battery reaction are easily
caused and there is therefore the possibility that a performance obtained
when a charge and discharge operation is repeated, that is, a cycle
performance is deteriorated. The total pore volume is more preferably in
the range of 0.11 mL/g or more and 0.4 mL/g or less.

[0048] The negative electrode is porous and comprises a negative electrode
current collector and a negative electrode active material-containing
layer which is supported on one or both surfaces of the current collector
and contains an active material, a binder and as required, a conductor.

[0049] As the negative electrode active material, a lithium compound that
absorbs and releases lithium ions is preferable. Examples of the lithium
compound include lithium oxides, lithium sulfides and lithium nitrides.
These compounds include compounds which contain no lithium in an
uncharged state but contain lithium when they are charged.

[0050] Examples of these oxides include metal oxides containing titanium
as the metal component, amorphous tin oxide such as
SnB0.4P0.6O3.1, tin-silicon oxides such as SnSiO3,
silicon oxide such as SiO and tungsten oxides such as WO3. Among
these compounds, metal oxides containing titanium as the metal component
are preferable.

[0051] Examples of the metal oxides containing titanium as the metal
component may include lithium-titanium oxides and titanium-based oxides
containing no lithium when synthesized. Examples of the lithium-titanium
oxides may include lithium titanate having a spinel structure and lithium
titanate having a ramsdellite structure. Examples of lithium titanate
having a spinel structure may include Li4+xTi5O12 (x
varies in the range: -1≦x≦3, depending on a
charge/discharge reaction). Examples of lithium titanate having a
ramsdellite structure may include Li2+yTi3O7 (y varies in
the range: -1≦y≦3, depending on a charge/discharge
reaction). Examples of the titanium-based oxides include TiO2 and
metal composite oxides containing Ti and at least one element selected
from the group consisting of P, V, Sn, Cu, Ni and Fe. TiO2 is
preferably of an anatase type that is heat-treated at a temperature of
300 to 500° C. to provide it with low crystallinity. Examples of
the metal composite oxides containing Ti and at least one element
selected from the group consisting of P, V, Sn, Cu, Ni and Fe may include
TiO2--P2O5, TiO2--V2O5,
TiO2--P2O5--SnO2 and TiO2--P2O5-MeO
(Me is at least one element selected from the group consisting of Cu, Ni
and Fe). This metal composite oxide preferably has low crystallinity and
has a microstructure in which a crystal phase and an amorphous phase
coexist or an amorphous phase exists independently. When the metal
composite oxide has such a microstructure, the cycle performance can be
greatly improved. Among these compounds, lithium-titanium oxide and metal
composite oxides containing Ti and at least one element selected from the
group consisting of P, V, Sn, Cu, Ni and Fe are preferable.

[0052] Examples of the sulfides include titanium sulfide such as
TiS2, molybdenum sulfide such as MoS2 and iron sulfides such as
FeS, FeS2 and LixFeS2 (0<x).

[0054] The negative electrode active material preferably contains at least
one type selected from lithium titanate having a spinel structure, such
as Li4+xTi5O12, FeS and FeS2. And the negative
electrode active material is most preferably lithium titanate having a
spinel structure. Because lithium titanate having a spinel structure has
excellent lithium-ion acceptability, a less resistant coating film can be
formed on the surface of the negative electrode by specifying initial
charge conditions.

[0057] The compounding ratio of the above negative electrode active
material, conductive agent and binder is preferably as follows: the
negative electrode active material: 80 to 98% by weight, the conductive
agent: 0 to 20% by weight and the binder: 2 to 7% by weight.

[0058] It is desirable for the current collector of the negative electrode
to be formed of aluminum foil or aluminum alloy foil. It is also
desirable for the current collector to have an average crystal grain size
not larger than 50 μm. In this case, the mechanical strength of the
current collector can be drastically increased so as to make it possible
to increase the density of the negative electrode by applying the
pressing under a high pressure to the negative electrode. As a result,
the battery capacity can be increased. Also, since it is possible to
prevent the dissolution and corrosion deterioration of the current
collector in an over-discharge cycle under an environment of a high
temperature not lower than, for example, 40° C., it is possible to
suppress the elevation in the impedance of the negative electrode.
Further, it is possible to improve the output performance, the rapid
charging performance, and the charge-discharge cycle performance of the
battery. It is more desirable for the average crystal grain size of the
current collector to be not larger than 30 μm, furthermore desirably,
not larger than 5 μm.

[0059] The average crystal grain size can be obtained as follows.
Specifically, the texture of the current collector surface is observed
with an electron microscope so as to obtain the number n of crystal
grains present within an area of 1 mm×1 mm. Then, the average
crystal grain area S is obtained from the formula "S=1×106/n
(μm2)", where n denotes the number of crystal grains noted above.
Further, the average crystal grain size d (μm) is calculated from the
area S by formula (A) given below:

d=2(S/π)1/2 (A)

[0060] The average crystal grain size of the aluminum foil or the aluminum
alloy foil can be complicatedly affected by many factors such as the
composition of the material, the impurities, the process conditions, the
history of the heat treatments and the heating conditions such as the
annealing conditions, and the crystal grain size can be adjusted by an
appropriate combination of the factors noted above during the
manufacturing process.

[0061] It is desirable for the aluminum foil or the aluminum alloy foil to
have a thickness not larger than 50 μm, more desirably not larger than
25 μm. Also, it is desirable for the aluminum foil to have a purity
not lower than 99%. It is desirable for the aluminum alloy to contain
another element such as magnesium, zinc or silicon. On the other hand, it
is desirable for the amount of the transition metal such as iron, copper,
nickel and chromium contained in the aluminum alloy to be not larger than
1%.

[0062] A production method of the negative electrode will be explained.
This negative electrode is manufactured by suspending the negative
electrode active material, conductive agent and binder in an appropriate
solvent and by applying this suspension to the current collector,
followed by drying and pressing to make a band-shaped material. The
process of preparing the suspension is important. In a so-called kneading
step in which the suspension is mixed in the condition of a low solvent
ratio, the temperature is set to 5 to 10° C. during kneading to
carry out this kneading process under a small shearing force for a time
as long as 12 hours to 18 hours, whereby finer flocks are sufficiently
pulverized. Moreover, the obtained suspension is circulated for 10 to 90
minutes by using a beads mill with a vessel having a capacity of A [L] at
a flow rate of A to 10 A [L/min] to make a suspension free from any
flock. At this time, the diameter of the beads is preferably 0.01 mmφ
or more and 0.45 mmφ or less. When the suspension as the product to
be treated is made to pass through the beads mill using small-diameter
beads at a large flow rate, that is, when the retention time during which
the suspension is made to pass one time through the vessel imparting a
small impact is shortened, only a soft shearing force is applied to the
suspension, making it possible to loosen the coagulation of primary
particles without any influence on the shape and crystallinity of the
negative electrode active material. When the diameter of the beads is
larger than 0.45 mmφ, there is a concern that too much energy is
applied to the suspension when the suspension is circulated through the
beads mill, causing easy coagulation among particles in the suspension,
on the contrary. Then, the suspension free from any flock is applied and
dried, whereby a negative electrode that satisfies the above conditions
(1) to (4) can be produced.

[0063] The positive electrode and nonaqueous electrolyte to be used in the
nonaqueous electrolyte battery will be explained.

[0064] 1) Positive Electrode

[0065] The positive electrode comprises a positive electrode current
collector and a positive electrode active material-containing layer which
is supported on one or both surfaces of the positive electrode current
collector and containing an active material, a conductive agent and a
binder.

[0066] This positive electrode is manufactured by adding the conductive
agent and the binder to the positive electrode active material,
suspending the mixture in an appropriate solvent and applying the
suspension to a current collector such as an aluminum foil, followed by
drying and pressing to make a band-shaped material.

[0068] Examples of the lithium-nickel-cobalt composite oxides include
LiNi1-y-zCoyM.sub.ZO2 (M is at least one element selected
from the group consisting of Al, Cr and Fe, 0≦y≦0.5 and
0≦z≦0.1). Examples of the lithium-manganese-cobalt
composite oxides include LiMn1-y-zCoyM.sub.zO2 (M is at
least one element selected from the group consisting of Al, Cr and Fe,
0≦y≦0.5 and 0≦z≦0.1). Examples of the
lithium-manganese-nickel composite oxides include
LiMnxNixM1-2xO2 (M is at least one element selected
from the group consisting of Co, Cr Al and Fe, 1/3≦x≦1/2).
Examples of the oxides represented by LiMnxNixM1-2xO2
include LiMn1/3Ni1/3Co1/3O2 and
LiMn1/2Ni1/2O2. Examples of lithium phosphates having an
olivine structure include LixFePO4,
LixFe1-yMnyPO4 and LixCoPO4.

[0074] The compounding ratio of the above positive electrode active
material, conductive agent and binder is preferably as follows: the
positive electrode active material: 80 to 95% by weight, the conductive
agent: 3 to 20% by weight and the binder: 2 to 7% by weight.

[0075] It is desirable for the current collector to be formed of an
aluminum foil or an aluminum alloy foil. It is desirable for the aluminum
foil or the aluminum alloy foil forming the current collector to have an
average crystal grain size not larger than 50 μm. It is more desirable
for the average crystal grain size noted above to be not larger than 30
μm, and furthermore desirably not larger than 5 μm. Where the
average crystal grain size of the aluminum foil or the aluminum alloy
foil forming the current collector is not larger than 50 μm, the
mechanical strength of the aluminum foil or the aluminum alloy foil can
be drastically increased to make it possible to press the positive
electrode with a high pressure. It follows that the density of the
positive electrode can be increased to increase the battery capacity.

[0076] It is desirable for the aluminum foil or the aluminum alloy foil to
have a thickness not larger than 50 μm, preferably not larger than 25
μm. Also, it is desirable for the aluminum foil to have a purity not
lower than 99%. Further, it is desirable for the aluminum alloy to
contain, for example, magnesium, zinc and silicon. On the other hand, it
is desirable for the content of the transition metals such as iron,
copper, nickel and chromium in the aluminum alloy to be not higher than
1%.

[0077] 2) Nonaqueous Electrolyte

[0078] This nonaqueous electrolyte contains a nonaqueous solvent and an
electrolyte salt to be dissolved in this nonaqueous solvent. Also, a
polymer may be contained in the nonaqueous solvent.

[0080] Here, the concentration of the electrolyte salt is preferably in
the range of 1.5 to 3M.

[0081] Examples of the nonaqueous solvent include, though not particularly
limited to, propylene carbonate (PC), ethylene carbonate (EC),
1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran
(THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolan, sulfolane,
acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC),
methylethyl carbonate (MEC) and dipropyl carbonate (DPC). These solvents
may be used either singly or in combination of two or more. Among these
solvents, γ-butyrolactone is preferable. Also, when two or more
solvents are combined, these solvents are all preferably selected from
those having a dielectric constant of 20 or more.

[0082] Additives may be added to this nonaqueous electrolyte. Examples of
these additives include, though not particularly limited to, vinylene
carbonate (VC), vinylene acetate (VA), vinylene butylate, vinylene
hexanate, vinylene crotonate and catechol carbonate. The concentration of
the additives is preferably in the range of 0.1 to 3 wt % with respect to
100 wt % of the nonaqueous electrolyte. A more preferable range is 0.5 to
1 wt %.

[0083] The structure of the nonaqueous electrolyte battery according to
the first embodiment is not particularly restricted, and may be various
structures such as a flat structure, a rectangular structure and a
cylindrical structure. An example of the flat nonaqueous electrolyte
battery is shown in FIGS. 2 to 4.

[0084] As shown in FIG. 2, an electrode group 1 has a structure in which a
positive electrode 2 and a negative electrode 3 are coiled in a flat
shape with interposition of a separator 4 between the electrodes. The
electrode group 1 is manufactured by applying hot-press after coiling the
positive electrode 2 and negative electrode 3 with interposition of the
separator 4 therebetween. The positive electrode 2, negative electrode 3
and separator 4 in the electrode group 1 may be integrated with an
adhesive polymer. A belt-like positive electrode terminal 5 is
electrically connected to the positive electrode 2, while a belt-like
negative electrode terminal 6 is electrically connected to the negative
electrode 3. The electrode group 1 is housed in a laminate film case 7
having heat-seal portions on three edges as an outer package member. The
tips of the positive electrode terminal 5 and negative electrode terminal
6 are pulled out from the shorter edge of the heat seal portion of the
case 7.

[0085] While the tips of the positive electrode terminal 5 and negative
electrode terminal 6 are pulled out from the same heat seal portion of
the case 7 as shown in FIG. 2, the heat seal portion from which the
positive electrode terminal 5 is pulled out may be different from the
heat seal portion from which the negative electrode terminal 6 is pulled
out. A specific example of the structure is shown in FIGS. 3 and 4.

[0086] As shown in FIG. 3, a laminated electrode group 8 is housed in the
case 7 made of the laminate film. As show in FIG. 4, the laminate film
comprises, for example, a resin layer 10, a thermoplastic resin layer 11,
and a metal layer 9 disposed between the resin layer 10 and thermoplastic
resin layer 11. The thermoplastic resin layer 11 is located on the inner
surface of the case 7. Heat-seal portions 7a, 7b and 7c are formed by
thermal adhesion of the thermoplastic resin layer 11 at one longer edge
and both shorter edges of the case 7 made of the laminate film. The case
7 is sealed with the heat-seal portions 7a, 7b and 7c. The laminated
electrode group 8 has a structure in which the positive electrodes 2 and
negative electrodes 3 are alternately laminated with interposition of the
separators 4 between them. Plural positive electrodes 2 are used, and
each electrode comprises a positive electrode current collector 2a and
positive electrode active material-containing layers 2b laminated on both
surfaces of the positive electrode current collector 2a. Plural negative
electrodes 3 are used, and each electrode comprises a negative electrode
current collector 3a and negative electrode active material-containing
layers 3b laminated on both surfaces of the negative electrode current
collector 3a. One edge of the negative electrode current collector 3a of
the negative electrode 3 is protruded out of the positive electrode 2.
The negative electrode current collector 3a protruded out of the positive
electrode 2 is electrically connected to the belt-like negative electrode
terminal 6. The tip of the belt-like negative electrode terminal 6 is
pulled out to the outside through the heat seal portion 7c of the case 7.
Both surfaces of the negative electrode terminal 6 are opposed to the
thermoplastic resin layers 11 that constitute the heat seal portion 7c.
An insulation film 12 is inserted between each surface of the negative
electrode terminal 6 and the thermoplastic resin layer 11 for improving
the bonding strength between the heat seal portion 7c and the negative
electrode terminal 6. An example of the insulation film 12 is a film
formed of a material prepared by adding an acid anhydride to a polyolefin
that contains at least one of polypropylene and polyethylene. The edge of
the positive electrode current collector 2a of the positive electrode 2
is protruded out of the negative electrode 3, although this configuration
is not illustrated in the drawing. The edge of the positive electrode
current collector 2a is positioned at an opposed side to the protruded
edge of the negative electrode current collector 3a. The positive
electrode current collector 2a protruded out of the negative electrode 3
is electrically connected to the belt-like positive electrode terminal 5.
The tip of the belt-like positive electrode terminal 5 is pulled out
through the heat seal portion 7b of the case 7. The insulation film 12 is
interposed between the positive electrode terminal 5 and the
thermoplastic resin layer 11 for improving bonding strength between the
heat seal portion 7b and the positive electrode terminal 5. The direction
in which the positive electrode terminal 5 is pulled out of the case 7 is
opposed to the direction in which the negative electrode terminal 6 is
pulled out of the case 7, as is evident from the above-described
construction.

[0087] As shown in FIGS. 3 and 4, a nonaqueous electrolyte battery
favorable for use under a large load current may be provided by providing
the pull-out direction of the positive electrode terminal 5 so as to be
opposed to the pull-out direction of the negative electrode terminal 6.

[0088] Examples of the structure of the electrode group include a coil
structure, as shown in FIG. 1 mentioned above, and a laminate structure
as shown in FIGS. 3 and 4 mentioned above. In the laminate structure, the
separator may be folded in a zigzag shape in use, as shown in FIG. 5. A
band-shaped separator 4 is folded in a zigzag shape. A negative electrode
31 strip is laminated on the top layer of the separator 4 folded in
a zigzag shape. A positive electrode 21 strip, a negative electrode
32 strip, a positive electrode 22 strip and a negative
electrode 33 strip are each inserted in this order from above into a
part where the separators 4 are overlapped on each other. The positive
electrodes 2 and the negative electrodes 3 are alternately arranged
between the separators 4 piled in a zigzag shape to thereby obtain an
electrode group having a laminate structure.

[0090] Examples of the material used for the separator may include porous
films containing polyethylene, polypropylene, cellulose or polyvinylidene
fluoride (PVdF) and synthetic resin nonwoven fabrics. Among these
materials, porous films made of polyethylene or polypropylene melt at a
fixed temperature to thereby cut off current and are therefore preferable
in terms of improving safety. Also, nonwoven fabrics made of cellulose
have a high porosity and therefore suppress clogging caused by a
resistant component in high-temperature storage.

[0091] The positive electrode terminal may be formed from materials having
electric stability and conductivity in a potential range of 3V to 5V with
respect to a lithium ion metal. Specific examples of the material include
aluminum and aluminum alloys containing elements such as Mg, Ti, Zn, Mn,
Fe, Cu and Si. It is preferable to use the same material that is used for
the positive electrode current collector to reduce the contact
resistance.

[0092] The negative electrode terminal may be formed from materials having
electric stability and conductivity in a potential range of 0.4V to 3V
with respect to a lithium ion metal. Specific examples of the material
include aluminum and aluminum alloys containing elements such as Mg, Ti,
Zn, Mn, Fe, Cu and Si. It is preferable to use the same material that is
used for the negative electrode current collector to reduce the contact
resistance.

[0093] A multilayer film comprising a metal foil covered with a resin film
may be used for the laminate film constituting the outer package member.
The resin available includes polymer films such as polypropylene (PP),
polyethylene (PE), nylon or polyethylene terephthalate (PET). As shown in
FIG. 4 above, polypropylene (PP) or polyethylene (PE) may be used as a
thermoplastic resin when one of the resin films is formed of the
thermoplastic resin. The metal foil can be formed of aluminum or an
aluminum alloy. The thickness of the laminate film is desirably 0.2 mm or
less.

[0094] While the outer package member made of the laminate film is used in
FIGS. 2 to 4, the material of the outer package member is not
particularly restricted and, for example, a case made of a metal with a
thickness of 0.5 mm or less may be used. The metal case available is a
rectangular or cylindrical metal can made of aluminum, an aluminum alloy,
iron or stainless steel. The thickness of the metal case is desirably 0.2
mm or less.

[0095] The aluminum alloy constituting the metal case is preferably an
alloy containing elements such as magnesium, zinc and silicon. However,
the content of transition metals such as iron, copper, nickel and
chromium is preferably 1% or less. This composition permits long term
reliability under a high temperature environment and heat dissipating
ability to be remarkably improved.

[0096] The metal can made of aluminum or an aluminum alloy preferably has
an average crystal grain size of 50 μm or less, more preferably 30
μm or less, and further preferably 5 μm or less. The strength of
the metal can made of aluminum or an aluminum alloy can be remarkably
increased by controlling the average crystal grain size to be 50 μm or
less to enable the can to be thin. Consequently, a vehicle-mounted
battery that is light weight, shows high output power and is excellent in
long term reliability can be realized.

[0097] FIG. 6 shows a nonaqueous electrolyte battery using a metal case
according to an embodiment.

[0098] The outer package member comprises a case 81 which has a bottomed
rectangular cylinder form and is made of aluminum or an aluminum alloy, a
lid 82 disposed on an opening part of the case 81 and a negative
electrode terminal 84 attached to the lid 82 through an insulating
material 83. The case 81 also serves as a positive electrode terminal. As
the above aluminum or aluminum alloy constituting the case 81, those
having the aforementioned composition and average crystal grain size may
be used.

[0099] An electrode group 85 is housed in the case 81. The electrode group
85 has a structure in which a positive electrode 86 and a negative
electrode 87 are coiled through a separator 88 in a flat form. This
electrode group 85 is obtained in the following manner: for example, a
band-like product obtained by laminating the positive electrode 86, the
separator 88 and the negative electrode 87 in this order is coiled in a
spiral form by using a plate or cylindrical core such that the positive
electrode 86 is positioned on the outside, and the obtained coiled
product is molded under pressure in the radial direction.

[0100] The nonaqueous electrolytic solution (liquid nonaqueous
electrolyte) is held in the electrode group 85. A spacer 90 which is
provided with a lead-takeoff hole 89 in the vicinity of the center
thereof and made of, for example, a synthetic resin is disposed on the
electrode group 85 in the case 81.

[0101] A takeoff hole 91 for the negative electrode terminal 84 is opened
in the vicinity of the center of the lid 82. A liquid injection port 92
is formed at a position apart from the takeoff hole 91 of the lid 82. The
liquid injection port 92 is sealed with a seal plug 93 after the
nonaqueous electrolytic solution is injected into the case 81. The
negative electrode terminal 84 is hermetically sealed in the takeoff hole
91 of the lid 82 through a glass or resin insulating material 83.

[0102] A negative electrode lead tab 94 is welded to the lower bottom
surface of the negative electrode terminal 84. The negative electrode
lead tab 94 is electrically connected to the negative electrode 87. One
end of a positive electrode lead 95 is electrically connected to the
positive electrode 86 and the other end thereof is welded to the lower
surface of the lid 82. An insulating paper 96 covers the entire outer
surface of the lid 82. An outer package tube 97 covers the entire side
surface of the case 81, and the upper and lower ends thereof are folded
so as to cover the upper and lower surfaces of the battery body,
respectively.

Second Embodiment

[0103] A battery pack according to a second embodiment comprises the
nonaqueous battery according to the first embodiment. The number of the
nonaqueous electrolyte batteries may be two or more. It is desirable that
the nonaqueous electrolyte battery according to the first embodiment be
used as a unit cell and each unit cell be arranged electrically in series
or in parallel to constitute a battery module.

[0104] The nonaqueous electrolyte battery according to the first
embodiment is suitable for use as a battery module and the battery pack
according to the second embodiment is superior in output performance and
cycle performance. The reason will be explained.

[0105] When the negative electrode is improved in nonaqueous electrolyte
impregnation ability and in the uniformity of the distribution of the
negative electrode active material, overvoltage is scarcely applied to
the negative electrode. As a result, the negative electrode can be
prevented from falling into a local overcharge or overdischarge state and
it is therefore possible to equalize the utilization factor of the
negative electrode active material. This makes it possible to greatly
reduce differences in capacity and impedance between unit cells
constituting the battery module. Specifically, in the battery module
obtained by connecting unit cells in series, a variation in voltage
between unit cells in a fully charged state is reduced because any
difference in capacities of the unit cells becomes small. Therefore, the
battery pack according to the second embodiment is superior in output
performance and can be improved in cycle performance.

[0106] Each of a plurality of unit cells 21 included in the battery pack
shown in FIG. 7 is formed of, though not limited to, a flattened type
nonaqueous electrolyte battery constructed as shown in FIG. 2. It is
possible to use the flattened type nonaqueous electrolyte battery shown
in FIGS. 3 and 6 as the unit cell 21. The plural unit cells 21 are
stacked one upon the other in the thickness direction in a manner to
align the protruding directions of the positive electrode terminals 5 and
the negative electrode terminals 6. As shown in FIG. 8, the unit cells 21
are connected in series to form a battery module 22. The unit cells 21
forming the battery module 22 are made integral by using an adhesive tape
23 as shown in FIG. 7.

[0107] A printed wiring board 24 is arranged on the side surface of the
battery module 22 toward which protrude the positive electrode terminals
5 and the negative electrode terminals 6. As shown in FIG. 8, a
thermistor 25, a protective circuit 26 and a terminal 27 for current
supply to the external equipment are connected to the printed wiring
board 24.

[0108] As shown in FIGS. 7 and 8, a wiring 28 on the side of the positive
electrodes of the battery module 22 is electrically connected to a
connector 29 on the side of the positive electrode of the protective
circuit 26 mounted to the printed wiring board 24. On the other hand, a
wiring 30 on the side of the negative electrodes of the battery module 22
is electrically connected to a connector 31 on the side of the negative
electrode of the protective circuit 26 mounted to the printed wiring
board 24.

[0109] The thermistor 25 detects the temperature of the unit cell 21 and
transmits the detection signal to the protective circuit 26. The
protective circuit 26 is capable of breaking a wiring 31a on the positive
side and a wiring 31b on the negative side, the wirings 31a and 31b being
stretched between the protective circuit 26 and the terminal 27 for
current supply to the external equipment. These wirings 31a and 31b are
broken by the protective circuit 26 under prescribed conditions
including, for example, the conditions that the temperature detected by
the thermistor is higher than a prescribed temperature, and that the
over-charging, over-discharging and over-current of the unit cell 21 have
been detected. The detecting method is applied to the unit cells 21 or to
the battery module 22. In the case of applying the detecting method to
each of the unit cells 21, it is possible to detect the battery voltage,
the positive electrode potential or the negative electrode potential. On
the other hand, where the positive electrode potential or the negative
electrode potential is detected, lithium metal electrodes used as
reference electrodes are inserted into the unit cells 21.

[0110] In the case of FIG. 8, a wiring 32 is connected to each of the unit
cells 21 for detecting the voltage, and the detection signal is
transmitted through these wirings 32 to the protective circuit 26.

[0111] Protective sheets 33 each formed of rubber or resin are arranged on
the three of the four sides of the battery module 22, though the
protective sheet 33 is not arranged on the side toward which protrude the
positive electrode terminals 5 and the negative electrode terminals 6. A
protective block 34 formed of rubber or resin is arranged in the
clearance between the side surface of the battery module 22 and the
printed wiring board 24.

[0112] The battery module 22 is housed in a container 35 together with
each of the protective sheets 33, the protective block 34 and the printed
wiring board 24. To be more specific, the protective sheets 33 are
arranged inside the two long sides of the container 35 and inside one
short side of the container 35. On the other hand, the printed wiring
board 24 is arranged along that short side of the container 35 which is
opposite to the short side along which one of the protective sheets 33 is
arranged. The battery module 22 is positioned within the space surrounded
by the three protective sheets 33 and the printed wiring board 24.
Further, a lid 36 is mounted to close the upper open edge of the
container 35.

[0113] Incidentally, it is possible to use a thermally shrinkable tube in
place of the adhesive tape 23 for fixing the battery module 22. In this
case, the protective sheets 33 are arranged on both sides of the battery
module 22 and, after the thermally shrinkable tube is wound about the
protective sheets, the tube is thermally shrunk to fix the battery module
22.

[0114] The unit cells 21 shown in FIGS. 7 and 8 are connected in series.
However, it is also possible to connect the unit cells 21 in parallel to
increase the cell capacity. Of course, it is possible to connect the
battery packs in series and in parallel.

[0115] Also, the embodiments of the battery pack can be changed
appropriately depending on the use of the battery pack.

[0116] The battery pack according to the second embodiment is preferably
used when good cycle performance is required at a large load current
(high current density). Specifically, the battery pack is used for power
sources of digital cameras, vehicle-mounted batteries for two-wheel or
four-wheel hybrid electric cars, two-wheel or four-wheel electric cars
and electric mopeds, and power sources of rechargeable vacuum cleaners.

Third Embodiment

[0117] The vehicle according to the third embodiment comprises the battery
pack according to the second embodiment. The vehicle as used herein
includes two-to four-wheel hybrid electric cars, from two- to four-wheel
electric cars, and motor-assisted bicycles.

[0118] FIGS. 9 to 11 show various type of hybrid vehicles in which an
internal combustion engine and a motor driven by a battery pack are used
in combination as the power source for the driving. The hybrid vehicle
can be roughly classified into three types depending on the combination
of the internal combustion engine and the electric motor.

[0119] FIG. 9 shows a hybrid vehicle 50 that is generally called a series
hybrid vehicle. The motive power of an internal combustion engine 51 is
once converted entirely into an electric power by a power generator 52,
and the electric power thus converted is stored in a battery pack 54 via
an inverter 53. The battery pack according to the second embodiment is
used as the battery pack 54. The electric power stored in the battery
pack 54 is supplied to an electric motor 55 via the inverter 53, with the
result that wheels 56 are driven by the electric motor 55. In other
words, the hybrid vehicle 50 shown in FIG. 9 represents a system in which
a power generator is incorporated into an electric vehicle. The internal
combustion engine can be operated under highly efficient conditions and
the kinetic energy of the internal combustion engine can be recovered as
the electric power. On the other hand, the wheels are driven by the
electric motor alone and, thus, the hybrid vehicle 50 requires an
electric motor of a high output. It is also necessary to use a battery
pack having a relatively large capacity. It is desirable for the rated
capacity of the battery pack to fall within a range of 5 to 50 Ah, more
desirably 10 to 20 Ah. Incidentally, the rated capacity noted above is
the capacity at the time when the battery pack is discharged at a rate of
0.2 C.

[0120] FIG. 10 shows the construction of a hybrid vehicle 57 that is
called a parallel hybrid vehicle. A reference numeral 58 shown in FIG. 10
denotes an electric motor that also acts as a power generator. The
internal combustion engine 51 drives mainly the wheels 56. The motive
power of the internal combustion engine 51 is converted in some cases
into an electric power by the power generator 58, and the battery pack 54
is charged by the electric power produced from the power generator 58. In
the starting stage or the accelerating stage at which the load is
increased, the driving force is supplemented by the electric motor 58.
The hybrid vehicle 57 shown in FIG. 10 represents a system based on the
ordinary vehicle. In this system, the fluctuation in the load of the
internal combustion engine 51 is suppressed so as to improve the
efficiency, and the regenerative power is also obtained. Since the wheels
56 are driven mainly by the internal combustion engine 51, the output of
the electric motor 58 can be determined arbitrarily depending on the
required ratio of the assistance. The system can be constructed even in
the case of using a relatively small electric motor 58 and a relatively
small battery pack 54. The rated capacity of the battery pack can be set
to fall within a range of 1 to 20 Ah, more desirably 3 to 10 Ah.

[0121] FIG. 11 shows the construction of a hybrid vehicle 59 that is
called a series-parallel hybrid vehicle, which utilizes in combination
both the series type system and the parallel type system. A power
dividing mechanism 60 included in the hybrid vehicle 59 divides the
output of the internal combustion engine 51 into the energy for the power
generation and the energy for the wheel driving. The series-parallel
hybrid vehicle 59 permits controlling the load of the engine more finely
than the parallel hybrid vehicle so as to improve the energy efficiency.

[0122] It is desirable for the rated capacity of the battery pack to fall
within a range of 1 to 20 Ah, more desirably 3 to 10 Ah.

[0123] It is desirable for the nominal voltage of the battery pack
included in the hybrid vehicles as shown in FIGS. 9 to 11 to fall within
a range of 200 to 600V.

[0124] It is desirable for the battery pack 54 to be arranged in general
in the site where the battery pack 54 is unlikely to be affected by the
change in the temperature of the outer atmosphere and unlikely to receive
an impact in the event of a collision. In, for example, a sedan type
automobile shown in FIG. 12, the battery pack 54 can be arranged within a
trunk room rearward of a rear seat 61. The battery pack 54 can also be
arranged below or behind the rear seat 61. Where the battery has a large
weight, it is desirable to arrange the battery pack 54 below the seat or
below the floor in order to lower the center of gravity of the
automobile.

[0125] An electric vehicle (EV) is driven by the energy stored in the
battery pack that is charged by the electric power supplied from outside
the vehicle. Since all the power required for the driving of the vehicle
is produced by an electric motor, it is necessary to use an electric
motor of a high output. In general, it is necessary to store all the
energy required for one driving in the battery pack by one charging. It
follows that it is necessary to use a battery pack having a very large
capacity. It is desirable for the rated capacity of the battery pack to
fall within a range of 100 to 500 Ah, more desirably 200 to 400 Ah.

[0126] The weight of the battery pack occupies a large ratio of the weight
of the vehicle. Therefore, it is desirable for the battery pack to be
arranged in a low position that is not markedly apart from the center of
gravity of the vehicle. For example, it is desirable for the battery pack
to be arranged below the floor of the vehicle. In order to allow the
battery pack to be charged in a short time with a large amount of the
electric power required for the one driving, it is necessary to use a
charger of a large capacity and a charging cable. Therefore, it is
desirable for the electric vehicle to be equipped with a charging
connector connecting the charger and the charging cable. A connector
utilizing the electric contact can be used as the charging connector. It
is also possible to use a non-contact type charging connector utilizing
the inductive coupling.

[0127] FIG. 13 exemplifies the construction of a hybrid motor bicycle 63.
It is possible to construct a hybrid motor bicycle 63 exhibiting a high
energy efficiency and equipped with an internal combustion engine 64, an
electric motor 65, and the battery pack 54 like the hybrid vehicle. The
internal combustion engine 64 drives mainly the wheels 66. In some cases,
the battery pack 54 is charged by utilizing a part of the motive power
generated from the internal combustion engine 64. In the starting stage
or the accelerating stage in which the load of the motor bicycle is
increased, the driving force of the motor bicycle is supplemented by the
electric motor 65. Since the wheels 66 are driven mainly by the internal
combustion engine 64, the output of the electric motor 65 can be
determined arbitrarily based on the required ratio of the supplement. The
electric motor 65 and the battery pack 54, which are relatively small,
can be used for constructing the system. It is desirable for the rated
capacity of the battery pack to fall within a range of 1 to 20 Ah, more
desirably 3 to 10 Ah.

[0128] FIG. 14 exemplifies the construction of an electric motor bicycle
67. The electric motor bicycle 67 is driven by the energy stored in the
battery pack 54 that is charged by the supply of the electric power from
the outside. Since all the driving force required for the driving the
motor bicycle 67 is generated from the electric motor 65, it is necessary
to use the electric motor 65 of a high output. Also, since it is
necessary for the battery pack to store all the energy required for one
driving by one charging, it is necessary to use a battery pack having a
relatively large capacity. It is desirable for the rated capacity of the
battery pack to fall within a range of 10 to 50 Ah, more desirably 15 to
30 Ah.

Fourth Embodiment

[0129] FIGS. 15 and 16 show an example of a rechargeable vacuum cleaner
according to a fourth embodiment. The rechargeable vacuum cleaner
comprises an operating panel 75 which selects operation modes, an
electrically driven blower 74 comprising a fun motor for generating
suction power for dust collection, and a control circuit 73. A battery
pack 72 according to the second embodiment as a power source for driving
these units are housed in a casing 70. When the battery pack is housed in
such a portable device, the battery pack is desirably fixed with
interposition of a buffer material in order to prevent the battery pack
from being affected by vibration. Known technologies may be applied for
maintaining the battery pack at an appropriate temperature. While a
battery charger 71 that also serves as a setting table functions as the
battery charger of the battery pack according to the second embodiment, a
part or all of the function of the battery charger may be housed in the
casing 70.

[0130] While the rechargeable vacuum cleaner consumes a large electric
power, the rated capacity of the battery pack is desirably in the range
of 2 to 10 Ah, more preferably 2 to 4 Ah, in terms of portability and
operation time. The nominal voltage of the battery pack is desirably in
the range of 40 to 80V.

[0131] The present invention will be explained in detail by way of
examples with reference to the drawings.

Example 1

Production of a Positive Electrode

[0132] LiCoO2 was used as a positive electrode active material, to
which were added a graphite powder as a conductive agent in an amount of
8% by weight based on the total amount of the positive electrode and PVdF
as a binder in an amount of 5% by weight based on the total amount of the
positive electrode. These components were dispersed in an
n-methylpyrrolidone (NMP) solvent to prepare a slurry. The obtained
slurry was applied to a 15-μm-thick aluminum foil, which was then
treated through drying and pressing processes to manufacture a positive
electrode having an electrode density of 3.3 g/cm3.

[0133] <Production of a Negative Electrode>

[0134] Li4Ti5O12 particles having a spinel structure and an
average particle diameter of 0.9 μm were prepared as a negative
electrode active material. To this negative electrode active material
were added graphite as a conductive agent in an amount of 10% by weight
based on the total amount of the negative electrode, and PVdF as a binder
in an amount of 3% by weight based on the total amount of the negative
electrode. These components were dispersed in an n-methylpyrrolidone
(NMP) solvent to prepare a slurry. The slurry was kneaded at 5° C.
for 18 hours. Furthermore, the kneaded slurry was subjected to a beads
mill process with a 1.7 L vessel to carry out circulation operation at a
flow rate of 3 L/min for 30 minutes. When the capacity of the vessel is A
(L), the flow rate corresponds to 1.8 A (L). At this time, 0.3 mmφ
zirconia beads were used. When the slurry as the product to be treated is
made to pass through the beads mill using small-diameter beads at a large
flow rate, that is, when the retention time during which the slurry is
made to pass one time through the vessel imparting a small impact is
shortened, only a soft shearing force is applied to the slurry, making it
possible to loosen the coagulation of primary particles without any
influence on the shape and crystallinity of the Li4Ti5O12
particles. Then, the obtained slurry was applied to a current collector
made of an aluminum foil 15 μm in thickness and dried, followed by
pressing, to produce a negative electrode having an electrode density of
2.1 g/cm3.

[0135] The distribution of pore size diameter of the obtained negative
electrode was measured by mercury porosimetry and as a result, the
specific surface area of pores calculated based on the weight of the
negative electrode, excluding the weight of the negative electrode
current collector, was 8.7 m2/g. The total pore volume per 1 g of
the negative electrode excluding the negative electrode current collector
was 0.1521 mL/g. The volume of pores having a diameter of 0.05 μm or
less per 1 g of the negative electrode excluding the negative electrode
current collector was 0.033 mL/g. Accordingly, the ratio of the volume of
pores having a pore size diameter of 0.05 μm or less to the total pore
volume was 21.70%. Also, the log differential intrusion curve had a peak
at a pore size diameter of 0.085 μm. Also, the above curve attenuated
with a decrease in pore size diameter from the apex present at a pore
size diameter of 0.085 μm.

[0136] <Preparation of a Nonaqueous Electrolyte>

[0137] 2M of LiBF4 was mixed in a mixture solvent prepared by
blending EC, PC and GBL in a ratio by volume of 1:1:4 to make a
nonaqueous electrolyte.

[0138] <Fabrication of a Battery>

[0139] A separator made of a polyethylene porous film was impregnated with
the nonaqueous electrolyte. The positive electrode was coated with this
separator. The negative electrode was overlapped on the positive
electrode with the separator therebetween, and the electrodes and
separator were coiled into a spiral form to manufacture a spiral
electrode group. This electrode group was pressed into a flat form. The
flattened electrode group was inserted into a can-shaped case made of
aluminum 0.3 mm in thickness to manufacture a 3.0-mm-thick, 35-mm-wide
and 62-mm-high flat-type nonaqueous electrolyte battery shown in FIG. 6.

[0140] After the obtained battery was charged up to 50% of the rated
value, it was discharged under 10 for 10 seconds. Thereafter, the battery
was recharged up to 50% of the rated value and then, it was discharged
under 5 C for 10 seconds. The current value when the voltage of the
battery reached 1.5V was found from the cutoff voltage in the 10
discharge operation and from the cutoff voltage in the 5 C discharge
operation by extrapolation. The power calculated from the current value
at 1.5V, that is, the maximum power among powers applied for 10 seconds
was 150 W.

[0141] The log differential intrusion curve and cumulative pore intrusion
curve, which showed the pore size diameter distribution of the negative
electrode measured by mercury porosimetry, were measured using the
methods described below.

[0142] An Autopore 9520 model, manufactured by Shimadzu Corporation, was
used as the measuring device. The negative electrode was cut into a size
of 25×25 mm2 to prepare a sample, which was then folded and
placed in a measuring cell for measurement under the condition of an
initial pressure of 20 kPa which corresponds to about 3 psia and also to
a pressure applied to a sample having a pore size diameter of about 60
μm. An average of three samples was used as the result of measurement.
In the adjustment of data, the specific surface area of pores was
calculated on the premise that the pore had a cylindrical form. When the
apex of a peak was present in a pore size diameter range of 0.03 μm to
0.2 μm in the log differential intrusion curve, the presence of the
peak in this range was recognized.

[0143] It should be noted that the analytical principle of the mercury
porosimetry is based on Washburn's equation (B):

D=-4γ cos θ/P Equation (B)

[0144] Here, P is a pressure to be applied, D is a pore size diameter,
γ is the surface tension of mercury and is 480 dynecm-1, and
θ is a contact angle of mercury with the wall surface of pores and
is 140°. γ and θ are constants and therefore, the
relation between the applied pressure P and the pore size diameter D is
found from Washburn's equation. If mercury penetration volume at this
time is measured, the pore size diameter and its volumetric distribution
can be found. As to the details of measuring method, principle and the
like, please refer to, for example, Motoji Zimpo et al., "Microparticle
Handbook" Asakura Shoten, (1991) and Sohachiro Hayakawa, "Powder Property
Measuring Method", Asakura Shoten (1978).

Examples 2 to 9 and Comparative Example 1

[0145] A battery was manufactured in the same manner as in Example 1
except that the flow rate when the negative electrode slurry was
circulated and the diameter of the beads were altered to those shown in
the following Table 1 and a negative electrode was used which had the
value shown in Table 1 as the result of measurement using mercury
porosimetry.

Example 10

[0146] A battery was produced in the same manner as in Example 1 except
that Li2Ti3O7 particles having an average particle
diameter of 0.5 μm were used as the negative electrode active
material.

Comparative Example 2

[0147] To the same negative electrode active material explained in Example
1 was added graphite as a conductive agent in an amount of 10% by weight
based on the total amount of the negative electrode, and PVdF as a binder
in an amount of 3% by weight based on the total amount of the negative
electrode. These components were dispersed in an n-methylpyrrolidone
(NMP) solvent to prepare a slurry. The slurry was kneaded and then, the
kneaded slurry was subjected to a beads mill process using zirconia beads
having a diameter of 1 mmφ to retain the slurry there for 60 minutes,
thereby applying a sufficient load on the slurry to disperse the slurry.
Then, the obtained slurry was applied to a current collector made of an
aluminum foil of 15 μm in thickness and dried, followed by pressing,
to produce a negative electrode having an electrode density of 2.1
g/cm3.

[0148] The pore size diameter distribution of the obtained negative
electrode was measured by mercury porosimetry and as a result, the
specific surface area of pores was 7.5 m2/g. The total pore volume
was 0.1734 mL/g. The volume of pores having a diameter of 0.05 μm or
less was 0.021 mL/g. Also, the log differential intrusion curve had a
peak at a pore size diameter of 0.083 μm. Also, the value of the log
differential intrusion decreased with a decrease in pore size diameter
from the apex present at a pore size diameter of 0.083 μm, but began
increasing at a pore size diameter of 0.02 μm to confirm a small peak
having an apex at a pore size diameter of 0.014 μm.

[0150] As is clear from Table 1, it is understood that each battery
obtained in Examples 1 to 10 using a negative electrode satisfying the
above conditions (1) to (4) is increased in the maximum power obtained by
outputting power for 10 seconds over that of each battery obtained in
Comparative Examples 1 and 2. The battery of Comparative Example 1 fails
to fulfill the condition (3). Since the ratio of the volume of pores
having a pore size diameter of 0.05 μm or less to the total pore
volume was less than 200, the maximum power was low. Also, in the case of
the negative electrode obtained in Comparative Example 2, the diameter of
the beads was increased to stir the slurry strongly and therefore, the
surface of primary particles of Li4Ti5O12 was scraped,
with the result that a second peak appeared at a pore size diameter
smaller than that at which the apex of the peak was present in the log
differential intrusion curve. Also, the ratio of the volume of pores
having a pore size diameter of 0.05 μm or less to the total pore
volume was less than 20%. Such a negative electrode was inferior in the
uniformity of the distribution of the negative electrode active material
and was therefore reduced in the maximum power.

[0151] Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects is
not limited to the specific details and representative embodiments shown
and described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their equivalents.